The present invention relates to plastic injection molds, and in particular, to nozzles and gates for the hot runner system of such injection molds.
Injection molds can have gates machined into either the cavity or core portion of the mold, or they can have separate gate inserts that are mounted in the mold cavity or core. The gates or gate inserts contain the nozzles that inject the hot plastic into the mold cavity. The nozzles are fed from manifolds that are part of the hot runner system for the injection mold.
In order to prevent the hot plastic being injected into the mold cavity from leaking back behind the nozzles during the injection process, it is necessary to provide a seal between the outlet end of the nozzle and the adjacent portions of the gate or gate insert. If the hot plastic does leak back behind the nozzle, it usually ruins any heating coils used to keep the nozzle hot, or it at least causes a time consuming clean up operation with consequent machine downtime.
It is difficult to get a good seal between the nozzle outlet or tip and the adjacent gate surfaces because the surface area of the mating components must be kept small to avoid too much heat loss. Further, the mating components are subject to wear because of thermal expansion and contraction during the molding process.
The present invention gives improved sealing by providing a double seal; a primary seal adjacent to the vestige and a secondary seal located behind the primary seal away from the nozzle outlet.
According to one aspect of the invention, there is provided a nozzle for use with a plastic injection mold gate defining a vestige. The nozzle comprises a main body portion including a central bore having an inlet portion, an enlarged threaded outlet portion and an annular shoulder separating the portions. A nozzle insert is located in the outlet portion and the insert includes an annular flange adapted to engage the annular shoulder. A hollow threaded insert retainer is threadably mounted in the outlet portion. The insert retainer has an inner annular shoulder for clamping engagement with the nozzle insert annular flange. An outer annular primary seal is adapted to sealingly engage the mold gate behind the vestige. An intermediate secondary sealing ring is adapted to sealingly engage the mold gate behind the primary seal.
According to another aspect of the invention, there is provided a gate insert and nozzle combination which comprises a hollow gate insert body defining a vestige. A first cavity is located behind the vestige and has an annular wall portion defining a primary sealing surface adjacent to the vestige. A second cavity is located behind the first cavity and has an annular wall portion defining a secondary sealing surface. A nozzle is located in the hollow gate insert body. The nozzle has a main body portion including a central bore having an inlet portion, an enlarged threaded outlet portion and an annular shoulder separating the portions. The nozzle also has a nozzle insert located in the outlet portion. The insert includes an annular flange adapted to engage the annular shoulder. The nozzle also includes a hollow threaded insert retainer threadably mounted in the outlet portion. The insert retainer has an inner annular shoulder for clamping engagement with the nozzle insert annular flange. An outer annular primary seal sealingly engages the gate insert primary sealing surface and an intermediate secondary sealing ring sealingly engages the gate insert secondary sealing surface.